Answer:
The 4th option. "Sarah rounded $6.95 and 9.5 down. Her estimate of $54 is too low."
Explanation:
Well, if you check Sara's math during option 4, you will find that when you round 6.95 and 9.5 down, you get 6 and 9.
If she would have done it correctly, she would have gotten "66. 025"
Therefore, 54 dollars is too low.